package contest1609;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Scanner;

public class ACheckAscendingOrder {
    static Scanner cin = new Scanner(new BufferedInputStream(System.in));//大量输入优化版本
    static PrintWriter cout = new PrintWriter(new BufferedOutputStream(System.out));//大量输出优化版本
    static PrintWriter cerr = new PrintWriter(System.err, true);//开启调试模式,一般输出量不大，不需要buffered

    public static void main(String[] args) {
        //TODO AOJ开启你的ACM传奇人生
        cerr.println("----Start your ACM legendary life with AOJ(www.webturing.com)----");
        int[] a = new int[100 + 50];
        int n = 0;
        while (cin.hasNextInt()) a[n++] = cin.nextInt();
        int[] b = a.clone();
        Arrays.sort(a, 0, n);
        if (Arrays.equals(a, b)) {
            cout.println("YES");
        } else {
            cout.println("NO");
        }

        cin.close();//关闭输入流
        cout.close();//关闭输出流，这是必须的，否则一般不会自动刷新缓冲区


    }

}
